Evidences of Roundup Ready Soybean Yield Drag in the US

Executive Summary

Over half the soybeans planted in the United States in 1999 are varieties genetically engineered to tolerate applications of the broad-spectrum, systemic post-emergence herbicide glyphosate manufactured by Monsanto Company (Trade Name, Roundup). Just a small fraction of soybeans produced in 1996 were “Roundup Ready” — varieties able to tolerate direct applications of glyphosate.

The rapid adoption of Roundup Ready (RR) soybeans has been unprecedented in the history of American row-crop agriculture. No new genetic trait, nor any pesticide has so dramatically gained market share in such a short period of time.

Roundup Ready soybeans have proven so popular with farmers because they greatly simplify the task of managing weeds and help farmers avoid a variety of problems associated with other herbicide-based weed management systems. They have proven especially popular among farmers who must complete weed management practices on a
timely basis over hundreds to thousands of acres of soybeans.

The success of RR soybeans is remarkable in light of the magnitude of the socalled Roundup Ready “yield drag.” Under most conditions extensive evidence shows that RR soybeans produce lower yields than possible if farmers planted comparable but non-engineered varieties.

This report reviews the results of over 8,200 university-based soybean varietal trials in 1998 and reaches the following conclusions regarding the magnitude of the RR soybean yield drag –
· The yield drag between top RR varieties compared to top conventional varieties averages 4.6 bushels per acre, or 6.7 percent.
· When comparing average yields across the top 5 varieties tested in 8 states, the yield drag averages 4.1 bushels, or 6.1 percent.
· Across all varieties tested, the yield drag averages 3.1 bushels, or 5.3 percent.
· In some areas of the Midwest, the best conventional variety sold by seed companies produces yields on average 10 percent or more higher than comparable Roundup Ready varieties sold by the same seed companies.

It is important to place the RR soybean yield drag in perspective. From 1975 to 1994 soybean yields rose on average about 0.5 bushels per year. In 1999 the RR soybean yield drag could result in perhaps a 2.0 to 2.5 percent reduction in national average
soybean yields, compared to what they would likely have been if seed companies had not dramatically shifted breeding priorities to focus on herbicide tolerance. If not reversed by future breeding enhancements, this downward shift in soybean yield potential could emerge as the most significant decline in a major crop ever associated with a single
genetic modification.

Ag BioTech InfoNet Technical Paper No 1
On whether RR soybean systems reduce pesticide use and increase grower profits, our analysis shows that –
· RR soybean systems are largely dependent on herbicides and hence are not likely to reduce herbicide use or reliance. Claims otherwise are based on incomplete information or analytically flawed comparisons that do not tell the whole story.
· Farmers growing RR soybeans used 2 to 5 times more herbicide measured in pounds applied per acre, compared to the other popular weed management systems used on most soybean fields not planted to RR varieties in 1998. RR herbicide use exceeds the level on many farms using multitactic Integrated Weed Management systems by a factor of 10 or more.
· There is clear evidence that Roundup use by farmers planting RR soybeans has risen markedly in 1999 because of the emergence of a degree of tolerance to Roundup in several key weed species, shifts in weeds toward those less sensitive to Roundup, price cuts and aggressive marketing.
· Roundup use on soybeans may well double from 1998 levels within the next few years. But if current trends continue in the way RR technology is used, the efficacy and market share of Roundup may then fall just as quickly.
· The RR soybean yield drag and technology fee impose a sizable indirect tax on the income of soybean producers, ranging from a few percent where RR varieties work best to over 12 percent of gross income per acre.

The remarkable popularity of Roundup Ready soybeans, despite their cost and the significant yield drag associated with their use, is evidence of the difficulty and high cost of today’s herbicide-dependent soybean weed management systems. The rapid evolution of weeds better able to withstand applications of Roundup reinforces the need for more integrated, multiple tactic weed management systems.

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